1. Field of the Invention
The present invention relates to a liquid level meter which detects and indicates level of various kinds of liquids such as gasoline, oil, petroleum, water and others stored in a tank or other various kinds of containers to be provided to automobiles and other machineries and apparatuses for industrial use. More specifically, the invention relates to an L-V conversion circuit which converts a change of inductance of a coil provided at the liquid level detecting part into a change of voltage.
2. Description of the Prior Art
A liquid-level meter of arm float type shown in FIG. 14 has been used. Such liquid level meter will be explained briefly. 101 is a set plate to be attached to a liquid container and a body 102 comprising a rotary potentiometer (not shown) is provided at the lower surface thereof. 103 is a float arm which is rotatably provided to the upper part of body 102 and a float 104 formed by a forming rubber is provided to the lower end of such float arm. The upper end of this float arm 103 is coupled so that it rotates said potentiometer.
105 is a float arm stopper provided to the body 102. 106 is a shaft extending downward from the lower surface of body 102, around which a cable 108 of a level switch is wound. 109 is an output cable.
Such arm float type liquid level meter has disadvantages; 1: accuracy is bad due to error in the shape of float arm 103 and loading accuracy, 2: accuracy in detection of position of float 104 generates dispersion due to friction at the bearing of float arm, 3: linearity between a rotating angle and liquid level is low because of a rotary type which is easily affected by swaying in the thrust direction to the shaft, 4: it is difficult to insert the meter into the container, and 5: the float arm 103 moves for the excessive range in the container, etc.
Moreover, the linear potentiometer type liquid level meters shown in FIG. 15 to FIG. 17 have also been used. Such liquid level meter will also be explained briefly. 110 is a set plate, 111 is a cylindrical case attached to the lower surface thereof. 112 is a bushing rubber attached to the lower end of case 111. At the center of such rubber, a hole 113 like a slit is formed and it is folded to the inside as shown in FIG. 17.
114 is a linear potentiometer provided within a case, coated with a common line 115 and a resistance pattern 116 formed like a rectangular wave as shown in FIG. 16. The lower end of the same linear potentiometer 114 is closely in contact with said hole 113. 117 is a float externally engaged with the linear potentiometer 114, short-circuitting between said common line 115 and resistance pattern 116. 118 is an air drain, and 119, 120 are liquid flowing holes.
Such linear potentiometer type liquid level meter has following disadvantages; namely, 1: accuracy is lowered by the effect of friction of float 117 to the linear potentiometer 114 on buoyancy of float 117, 2: a float 117 becomes large in size 3: a case 111 is necessary for avoiding the swaying of float 117 as much as possible, 4: dust is easily adhered because a linear potentiometer 114 is exposed and the resistance materials 115, 116 have uneven surfaces, and 5: poor contact may occur and the float may catch somewhere.